This HOWTO describes the needed setup to control a MIDI capable software synthesizer from a MIDI sequencer
through a virtual MIDI connection under ALSA 0.9. This document can be freely translated and distributed. It's
released under the GNU Free Documentation License.

Software synthesizers like Csound, PD, jMax or Spiral Synth Modular offer nearly endless freedom to create known
or unknown, common or unusual sound experiences. They can also replace pricy hardware synths or the inexpensive,
often bad-sounding MIDI synths on some soundcards, if these are supported under Linux at all. On the other hand,
composing inside those softsynths can be a tedious task: in Csound for example one has to write endless rows of
numbers in a spreadsheet-like manner - not a comfortable way to make music.

MIDI sequencer applications are more suitable for this task. They provide an interface to insert notes and control
data in convenient ways: as notes in a real score, as marks in a piano roll or as a list of MIDI events, if you prefer this
view. Another kind of MIDI sequencers offer a tracker-like way of entering notes, like many people are used to from
the good old days when that was the state of art in the Scene. Last but not least, some MIDI sequencers allow you to
record your own playing on a keyboard or on another physical device, which is for many users the most natural way of
writing music.

But MIDI sequencers like to output their notes to MIDI devices that normally route their events to the outside world,
i.e., to hardware synths and samplers. With virtual MIDI devices one can keep the MIDI data inside the computer and
let it control other software running on the same machine. This HOWTO describes all that is necessary to achieve
this goal.

In our setup we use the ALSA library and driver modules, as this is (or should be) the standard way of doing serious
audio and MIDI on Linux. The tutorial assumes that we are running the 0.9.0 branch of ALSA, but the virtual MIDI
module was also present in ALSA 0.5.x so most of the following should apply for this as well. In the OSS/Free (the
sound modules found in kernels previous to the 2.5.x track) and OSS/Linux sound architectures the v_midi module
can be used, but this is beyond the scope of this document.

To use ALSA's virtual MIDI card the snd-card-virmidi module must be present. In the most recent versions of
ALSA (and in the 2.5.x development kernel) that module lost its '-card' middle-fix and was renamed to
snd-virmidi. Make sure that you did build this module, it might be missing if you configured ALSA to build only the
modules for your actual card(s).

The virmidi module has to be loaded to make the virtual MIDI ports available. You can test-load it by hand with

$ modprobe snd-virmidi snd_index=1

where snd_index is set appropriately to the first free card index (=1 if you have only one card that already has index
0), but it is more convenient to adapt your modules configuration to have it sitting around already when you need it.
For that we need to extend the ALSA section in /etc/modules.conf (or in another location, depending on your
distribution) with the following:

Now you have configured a virtual MIDI card as the second card with index 1, assuming you have one real soundcard
(which would be very useful). If you have a second real card like I do, change the configuration above to read:

The devices starting with '2-' are my virtual MIDI devices. Yours would start with '1-' if you only had one physical
card in your system.

You can get a nicer listing with ALSA's own aconnect utility, which we will need anyway. Called with option -o (or
-lo) it will show the MIDI devices capable of MIDI output, while a call with -i shows those with MIDI input
capabilities:

The devices shown correspond to ALSA's own OSS-compatible raw MIDI devices in the /proc/asound/dev directory
tree. For example /proc/asound/dev/midiC2D0 is the first MIDI device of our virtual MIDI card at index 2, called
Virtual Raw MIDI 2-0 by aconnect. In Debian those devices are available in /dev/snd/ as well, and they also are
internally linked with the old OSS device locations: /dev/midiXX. To make sure that I can get the ALSA raw MIDI
ports from /dev/midiXX I symlinked them with

Now that we have created and configured a VirtualMIDI card we can use it in our applications just like any other
MIDI devices. Just insert the needed device, be it an OSS-compatible /dev/midi20 or an ALSA MIDI port like 80:0,
at the correct configuration point of your favourite sequencer and synthesizer application.

aconnect

Without further arrangements we will not be able to send the MIDI events from our sequencer to a softsynth. For
that, we first need to connect two ports with (you guessed it) the aconnect utility. This tool connects two or more
ports. Its -i and -o output above has already shown us the available ports, and with a simple syntax these can now be
connected in a one-way fashion:

$ aconnect [sender port] [receiver port]
$ aconnect 80:0 81:0

This routes all MIDI data sent to port 80:0 over to port 80:1. In our setup this means that every event coming in at
/dev/midi20 gets sent to /dev/midi21, where it can be read ('received') by another application.

If you had configured the VirMIDI card as your second card (with card index 1) you should have these ports:

You see that 'Virtual Raw MIDI 1-0' now is connected to 'Virtual Raw MIDI 1-1'. Now, depending on your
applications, you can read MIDI data that was sent to 'Virtual Raw MIDI 1-0' from 'Virtual Raw MIDI 1-1', or in
OSS-device speak: What was sent to /dev/midi10 gets routed to /dev/midi11 and can be read from there.

You can also connect more than one port to a port. If you call aconnect twice like this:

$ aconnect 72:0 73:0
$ aconnect 72:0 74:0

you can receive the same data send to /dev/midi10 at /dev/midi11 and at /dev/midi12 as well. And of course you can
really hammer your machine if you create more VirMIDI cards and wildly connect these. There's no stopping us
now...

Bob Ham's ALSA MIDI Patch Bay is a very useful graphic frontend to ALSA's MIDI connection setup. Usage is very
simple and intuitive: On the left are the MIDI ports that are capable of sending MIDI events, while on the right you
see the ports with receiving capability. If you click on a left-side port it gets selected for a new connection to the port
on the right that you click next. Clicking on a right-side port will disconnect the port if it was connected. A clean and
easy tool that has the potential to redundantize this HOWTO. ;)

aseqview

Another useful tool for routing MIDI events is aseqview by ALSA developer Takashi Iwai. You can download it at
Iwai-sama's homepage http//members.tripod.de/iwai/alsa.html, but it is also included in many distributions. This
graphic utility was designed to view and change MIDI events as they pass through your computer, but it also has the
capability to route events to different MIDI ports like aconnect does. This comes in handy when you have to deal with
applications that use the OSS sequencer device, which aconnect is sometimes unable to reach. If you start aseqview
without any options you get a nice GUI and a new MIDI port. The default is port 128:0, and it looks like this:

client 128: 'MIDI Viewer' [type=user]
0 'Viewer Port 0 '

With this port all the aconnect tricks that we have seen by now are possible. But if you just need to connect the
aseqview port to another port, aseqview can do this by itself with the -d option :

$ aseqview -d 73:0 &

This connects port 128:0 (if that was available) to port 73:0 right from the start of aseqview.

There are some more graphical aconnect tools with very similar functionality. Maarten de Boer used most af the original aconnect source code to write a graphical frontend called "aconnectgui" with the FLTK toolkit. It is available at
http://www.iua.upf.es/~mdeboer/. His software has the best looks, in my opinion.

Personally I use kaconnect, maybe because it has the shortest name, that is the fastest to type. kaconnect was developed by Suse's own Dr. Matthias Nagorni as a part of his series of tools and softsynths for ALSA, the kalsatools. Don't let the "k" in the name fool you, the software does not require KDE, it uses the pure QT GUI libraries. kaconnect and more is available at
http://www.suse.de/~mana/kalsatools.html.

In this last section I will show some examples, how to use the virtual MIDI connections in various applications. I will
assume a VirMIDI card as a third card in the system, using ALSA MIDI ports 80:0 to 83:0 that correspond to the raw
OSS MIDI devices /dev/midi20 to /dev/midi23 and to the ALSA raw MIDI devices /dev/snd/midiC2D0 to
/dev/snd/midiC2D3. Of these, the first two have been 'aconnected' with

$ aconnect 80:0 81:0

As shown, this means, that all MIDI data sent to /dev/midi20 (or port 80:0 or /dev/snd/midiC2D0) can now be read at
/dev/midi21 (or port 80:1 or /dev/snd/midiC2D1)

MusE

MusE is a full-featured MIDI sequencer written by Werner Schweer, available at http://muse.seh.de. We will need to
configure the the virtual MIDI port as an output port in the section 'Config->MIDI Ports'. In MusE, the ports are
named by their ALSA names 'VirMIDI X-X':

Now make sure that the right port is selected as the output port for the channel on which you want the software
synthesizer to listen to and play the MIDI events:

For some reason I could not use 'VirMIDI 2-0' as output device in MusE 0.4.9. That is the expected device when I
wanted to receive on 'VirMIDI 2-1' but I had to use it the other way around. I don't know why, I'm probably stupid,
and you might have to experiment a bit. One could also use the midi02 or midi2 devices.

ttrk

Billy Biggs's ttrk is a simple, quick and tight MIDI sequencer with a tracker interface. It can output its MIDI data to
any MIDI port configured in the file $HOME/.ttrkrc.

Put this line there to have ttrk write to /dev/snd/midiC2D0:
and you're good to go...

Shaketracker

Juan Linietsky's Shaketracker revives the MIDI tracker interface like ttrk, but it has a more complete translation of
the classic tracker effects to MIDI data. Unfortunatly it uses the OSS sequencer device (/dev/sequencer) for its MIDI
output, not the raw MIDI devices, and I could not get it to work with aconnect. But there is a workaround that
involves aseqview. If we start aseqview before Shaketracker, the tracker will recognize and use the aseqview port. One
just has to select it in the 'User Devices' section of Shaketracker, where it shows up by its ALSA name 'Viewer Port
0':

It is convenient to give this User Device a good name instead of 'Null Output'.

If we start aseqview without options we would need to aconnect the aseqview port with the softsynth port, but as
shown previously we could also start aseqview directly with a destination port. Don't forget to use the new User
Device in every track that should go to the softsynth. I always run Shaketracker with a little shell script that starts
aseqview, waits for the creation of ports, and then starts Shaketracker:

Pure Data

Miller Puckette is the genius behind the open-source software synthesis and multimedia development environment
Pure Data (PD), which evolved out of MAX and in turn was the basis for the MAX-extension MSP. PD can use raw
MIDI devices to read MIDI events that are specified with the option '-midiindev <devnumber>' but it has an
irritating way of specifying which device to use. The formula is as follows: To use /dev/midi0, start PD with 'midiindev
1', to use /dev/midi1 start it with '-midiindev 2' and so on. Got it? You must specify the real device number plus 1
here. Another example: For /dev/midi21 start PD with '-midiindev 22'

PD has a help patch 'Test audio and MIDI', that is invaluable in locating the right MIDI device:

Csound

Csound is the grandmother of most of todays software synthesizers, and it has learned MIDI as well. Running 'csound
--help' shows where one has to configure the MIDI input device:

Conclusion

By now you should know how to use a software synthesizer to orchestrate music composed in and played by a MIDI
sequencer. Of course, tools like aconnect and aseqview don't need to be used with a MIDI software sequencer. You
could also redirect events that come into your machine from an external sequencer or from an external MIDI
keyboard directly to the software synth without the MIDI sequencer step. Just 'aconnect' the external MIDI device to
your softsynth or to the on-board synth of your soundcard. Or go the other way around: PD, Csound or environments
like KeyKit allow you to create MIDI events in algorithmic ways that are nearly impossible with classic Cubase-like
MIDI sequencers. With aconnect you can route these events to any MIDI capable sound module you have.